The present invention relates to a friction clutch, in particular for a motor vehicle, and more particularly it relates to a clutch which is equipped with a device for compensating for wear which is due in particular to wear of at least one friction liner, the said device, which is hereinafter called a wear compensating device, operating in response to the wear which takes place in the liner or liners.
A conventional friction clutch generally includes a reaction plate which is part of an engine flywheel, which may be in two parts so as to constitute a damping flywheel or a flexible flywheel, mounted in rotation on a first shaft which is usually a driving shaft, such as the crankshaft of the internal combustion engine, and which supports, through its outer periphery, a cover plate to which at least one pressure plate is attached.
The pressure plate is fixed to the cover plate and reaction plate for rotation with them, while being axially displaceable under the biasing action of axially acting clutch engaging means controlled by declutching means; the clutch engaging means may consist of helical springs or one or two Belleville rings mounted in series or in parallel and subjected to the action of declutching levers which constitute the declutching means; generally the clutch engaging and declutching means are incorporated in a single component, for example a metallic diaphragm which bears on the cover plate; the diaphragm may be mounted in series or in parallel with a Belleville ring to assist the declutching force.
A friction disc, carrying at least one friction liner at its outer periphery, and fixed to a shaft for rotation therewith, the shaft being usually a driven shaft such as the input shaft of the gearbox, is interposed between the pressure plate and reaction plate in such a way as to be gripped between them when the clutch is in its disengaged condition. The clutch engaging means control the axial displacement of the pressure plate when they are actuated by a clutch release bearing through the declutching means.
The friction disc usually comprises a support disc which is elastic in the axial sense, and on either side of which two friction liners are fixed. Gripping of the friction disc is thus progressive. In other versions the support disc is rigid, and is for example encapsulated at its outer periphery within a friction liner.
During the working life of such a clutch, the friction liner or liners and the counteracting elements, that is to say the pressure plate and reaction plate, undergo wear which causes the position of the pressure plate and the positions of the axially acting clutch engaging means and clutch release bearing to vary, from which there follows a variation in the gripping force exerted between the friction disc on the one hand and the pressure and reaction plates on the other, due to the modifications in the working conditions of the clutch engaging means, and the force necessary to effect declutching is thereby affected. By giving such a clutch a wear compensating device, these disadvantages are avoided, with the clutch engaging means and the clutch release bearing, which is usually in constant engagement on the declutching means, occupying the same position when the clutch is in its engaged state, so that the axial size of the clutch is reduced.
It is known to provide, in particular for a motor vehicle, a friction clutch of the kind comprising a reaction plate adapted to be mounted in rotation on a driving shaft, a friction disc carrying at its outer periphery at least one friction liner and adapted to be mounted in rotation on a driven shaft, a pressure plate, a cover plate fixed on the reaction plate, axially acting clutch engaging means which are controlled by declutching means and which work between the cover plate on the one hand and the pressure plate on the other hand, through secondary abutment means and primary abutment means, the pressure plate being fixed in rotation to the cover plate while being displaceable axially with respect to the latter and being subjected to the action of resilient return means urging the pressure plate axially towards the cover plate, the said clutch further including a wear compensating device comprising ramp means, the ramps of which are disposed circumferentially and which is placed axially between the abutment means and the pressure plate and adapted to cooperate with counter-ramp means, a set of teeth with which a worm disposed tangentially is in cooperation, the ramp means being fixed in rotation to the said set of teeth, means being provided for driving the worm in rotation and being operated as a result of wear in the friction liner or liners when the clutch is engaged, the said worm driving means consisting of a ratchet wheel which is fixed in rotation to the worm and being controlled through a control tongue which is part of a resilient member, the worm and the ratchet wheel being carried by a support member, the support member and the resilient member being fixed to the cover plate and being placed inside the latter, the support member being U-shaped with a spine and two wings which are adapted to support a spindle carrying the worm and the ratchet wheel.
A clutch of this kind is for example described in the document FR-A-2 753 503.
Up to the present time in such a clutch, the resilient member is supported by the spindle through two ears of the resilient member, which are formed with holes through which the said spindle passes in the vicinity of the ends of the latter; such an arrangement works well. However, it can be desirable, firstly to simplify the resilient member, and secondly to increase the length of the control tongue so as to reduce the stresses that may affect its useful life expectancy.
An object of the present invention is to respond to these desires in a simple and inexpensive way.
Thus, in accordance with the invention a clutch of the above type is characterised by the fact that the resilient member is fixed to the spine of the support member independently of the fastening of the support member to the cover plate.
Preferably, the resilient member is disposed at least partly in the zone in which it is fixed to the support member, between the spine of the support member and the cover plate.
The length of the control tongue can then be increased and the latter is subjected to less stress. The resilient member is simplified because it does not have wings in contact with the wings of the support member.
Preferably, the resilient member is generally U-shaped in axial cross section and comprises two axially oriented wings, one of which is formed with a hole for fastening it to the support member, for example by riveting or clipping, the other one being configured as a control tongue and extending generally parallel to the axis of the clutch.
In one embodiment, the spine of the support member is extended, beyond the wings, by a transverse flange extending generally at right angles to the spine and wings, while the wing of the resilient member, for fastening the latter to the support member, is extended by a generally perpendicular tongue which extends outwards from the fixed U, and, with the flange of the support member, lies against a transverse flange of the cover plate.
Preferably, the course of travel of the control tongue with respect to the ratchet wheel, during the operation of disengaging the clutch, is limited by a control abutment defined by at least one lug formed by being pressed out in the support member.
Preferably, the edge of the spine of the support member is cut out in the centre as a slot having a width with which the corresponding width of the resilient member, which is fitted in the slot, is matched; in a preferred embodiment, a lip is formed at the base of the slot, the lip having a rounded end and a concavity directed towards the inside of the wings of the support member: with this arrangement the control tongue can roll around the lip in operation, and its deformation is progressive, which increases its useful life even more.
Preferably, the spine of the resilient member, which joins its wings together, has, in line with its junction with the wing which is configured as a control tongue, a widened zone which is adapted to come into abutment on the control abutment of the support member.
Preferably, the axially acting clutch engaging means consist of a diaphragm.
In a preferred embodiment, the primary abutment means consist of a circumferential press-formed element, continuous or fragmented, formed in the base portion of the cover plate.
Preferably, the ratchet wheel is controlled by the diaphragm through the control tongue; the ratchet wheel is controlled by an actuator consisting of an appendix of the diaphragm at its outer periphery; two lugs are provided, and are spaced circumferentially apart by a passage for the actuator.
Preferably, the ramp means consist of an annular ring having, on one axial side, the inclined ramps which are spaced apart circumferentially, and on the other axial side, the secondary abutment means.
Preferably, the counter ramp means consist of pads adapted to cooperate with the ramps of the ramp means.
Preferably, the worm is mounted for displacement along its axis when subjected to the action of a so-called resilient take-up means.